The present invention relates to a throttle control apparatus for an internal combustion engine and particularly to such a control apparatus for outboard motors and the like.
Outboard motors generally include a powerhead secured to the upper end of a driveshaft housing which is provided with a swivel bracket mounting means for attaching of the outboard motor to the transom of a boat. A dependent propeller unit is secured to the lower end of the driveshaft housing and coupled by a drive shaft which extends upwardly through the driveshaft housing to an internal combustion engine mounted within the powerhead. The internal combustion engine is generally a conventional reciprocating piston type having one or more cylinders each of which includes a spark plug for firing of the fuel mixture at an appropriate time with respect to the top dead center (TDC) position of the piston. The fuel mixture supplied to the engine is further controlled by a throttle control means for varying the speed of the engine. The throttle control apparatus may be remotely controlled or in lower horsepower outboards may be controlled through a tiller handle secured to the outboard for pivoted securing of the outboard. The tiller is formed conventionally with a twist grip mechanically coupled to the throttle control. For optimum operation, the firing time of the engine varies slightly as the engine speed is increased. Generally, the timing desired includes a slight retarded firing at idle speed such that the spark plug is fired slightly after the piston reaches TDC. When the engine is accelerated, the control preferably advances the firing to TDC before the throttle control is actuated to increase the fuel supply to the engine. As the engine speed is further increased, the firing timing is advanced before TDC and preferably with the advance being rapidly established for a relatively slight throttle advance; after which the timing is held constant for the remainder throttle range, and for a greater share of the throttle range. Various interconnecting linkages have been suggested for controlling the timing advance in relationship to the actuation of throttle butterfly valve of the engine carburetor. For example, the copending application of Beck et al which is entitled "Breakerless and Distributorless Multiple Cylinder Ignition System" which was filed on July 18, 1973 with Serial No. 380,384 and which is assigned to the same assignee as the present application, discloses a trigger coil arrangement for controlling the firing of the spark plugs. The trigger coil is rotatably mounted about the crankshaft and coupled through a cam arrangement to the throttle lever to vary the position of the coil about the axis of the crankshaft and thereby provide timing control. In such systems, adjustable linkage systems are employed to permit adjustment for normal manufacturing tolerances and the like. Further, the linkage system should provide a relatively simple mechanical system which will have a long operating life under the relatively severe vibrational environment encountered in outboard motors and the like. In small outboards the available space is quite restricted and a small, compact linkage is desirable.